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N-Acetylcysteine, the Obscure Antioxidant

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N-Acetylcysteine, the Obscure Antioxidant

Majid Koozehchian, M.S.

The antioxidant N-acetylcysteine (NAC), a modified form of essential amino acid cysteine, which is both consumed in high-protein food and synthesized in the body, does not receive much attention but has important, positive impacts in the body (1). This antioxidant is a precursor to glutathione (the master antioxidant) in the body, and is readily metabolized into intracellular glutathione.



Following are some benefits reported for NAC:


  • NAC protects the body from acetaminophen toxicity (e.g. Tylenol) and can be used for patients with acetaminophen poisoning. NAC has a role in treating acetaminophen-related acute liver failure (2).
  • NAC assists the body in maintaining healthy homocysteine levels (an amino acid that in high amounts is related to heart disease) (3).
  • NAC supports lung and bronchial health. It works in the sinus and nasal passages to assist in breaking up thick mucus that cannot flush out irritants (4).
  • NAC supports the immune system function via its effects on generation and release of cytokines (a protein with some effects on interactions between cells).
  •  NAC also strengthens the immune system through inhibiting or reducing kidney damage and helps the liver eliminate toxins (5).
  • NAC supports the proper functioning of B cells, T cells, and phagocytes, which are important for HIV and pneumonia patients (6).
  • NAC reduces progression of multiple sclerosis (a progressive disease of the brain, the spinal cord, and the optic nerves) (7).








NAC and Exercise


NAC as an antioxidant improves the ability to recover from exercise and various stresses. Some studies show that NAC supplements result in improved performance by reducing oxidative stress, a causal factor in the fatigue process.


  • While a study by Michael Reid et al. indicates that NAC has no impact on force production during extreme muscle contractions, other findings reveal that NAC reduces and prevents glutathione oxidation during aerobic exercise. Therefore, NAC may be helpful in delaying fatigue and producing oxidative stress (8).
  • Medved et al. demonstrated that NAC infusion in young healthy men increases the time to exhaustion in prolonged aerobic exercise (9).
  • Kerksick and Willoughby noted that NAC is an effective free radical scavenger and a primary contributor to maintenance of the cellular glutathione status in muscle cells. NAC can minimize fatigue or extend the time it takes for fatigue to accumulate, as well as prevent the onset of apoptosis (programmed cell death) secondary to exhaustive exercise (10).





Dietary Sources and Recommended Daily Allowance (RDA) for NAC


NAC is made by the human liver by altering the amino acid cysteine and can be found in high-protein foods, such as meat, fish, seafood, chicken or turkey. Minor sources are eggs, whole-grain products such as breads and cereals, and some plants including broccoli, onions, and legumes. There is no RDA for NAC, but 250-1500mg/day has been used in clinical studies with no adverse effects reported. NAC-deficiency does not appear to result in any serious disorders, nor has NAC overdose shown toxicity. However, it may elevate the amount of zinc released in the urine; therefore, those who use NAC supplements for more than a month should make sure to take one that contains zinc. NAC is most effective when consumed on an empty stomach (9, 10).





Various findings report that NAC (a) supports lung and bronchial health, (b) prevents glutathione oxidation, and (c) minimizes muscle fatigue. NAC’s other possible roles in muscle damage, multiple sclerosis, and HIV infection are currently being studied.




Related Articles


  1.  (10/18/2012)
  2. Lee WM, Hynan LS, Rossaro L, Fontana RJ, Stravitz RT, Larson AM, et al. Intravenous N-acetylcysteine improves transplant-free survival in early stage non-acetaminophen acute liver failure. Gastroenterology 2009 Sep;137(3):856-64, 864.e1.
  3. (10/17/2012)
  4. Stey C, Steurer J, Bachmann S, Medici TC, Tramer MR. The effect of oral N-acetylcysteine in chronic bronchitis: a quantitative systematic review. Eur Respir J 2000 Aug;16(2):253-262.
  5. (10/18/2012)
  6. (10/21/2012)
  7. N-acetyl-L-cysteine ameliorates the inflammatory disease process in experimental autoimmune encephalomyelitis in Lewis rats. Available at: Accessed 11/25/2012, 2012.
  8. Reid MB, Stokic DS, Koch SM, Khawli FA, Leis AA. N-acetylcysteine inhibits muscle fatigue in humans. J Clin Invest 1994 Dec;94(6):2468-2474.
  9. Medved I, Brown MJ, Bjorksten AR, Murphy KT, Petersen AC, Sostaric S, et al. N-acetylcysteine enhances muscle cysteine and glutathione availability and attenuates fatigue during prolonged exercise in endurance-trained individuals. J Appl Physiol 2004 Oct;97(4):1477-1485.
  10. Kerksick C, Willoughby D. The antioxidant role of glutathione and N-acetyl-cysteine supplements and exercise-induced oxidative stress. J Int Soc Sports Nutr 2005 Dec 9;2:38-44.



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